The dominant copper-containing minerals in most copper sulfide deposits are chalcopyrite, cubanite and bornite. Chalcocite and, in some cases, covelite may also be present in ores and recovered into concentrates. The gangue minerals includes sulfides, sometimes have pyrite and pyrrohotite, along with lesser quantities of host rock or gangue silicate minerals report to the final flotation concentrate. Impurity elements such as arsenic and antimony may also be contained in these minerals, or additionally as energite, tennantite and tetrahedrite, which classifies the concentrates as “dirty” with respect to smelting of the concentrates. Such “dirty” concentrates may have penalties imposed by purchasers, or be rejected for treatment.
High-grade copper sulfide concentrates (typically greater than about 25% Cu) are commonly treated by pyrometallurgical routes, whereas hydrometallurgical routes are generally favoured for the lower-grade copper concentrates and “dirty” concentrates. The economically and technically most favourable processing route can also be influenced by the concentration of minor metals such as cobalt and nickel, valuable metals such as silver, gold, palladium and platinum, as well as deleterious metals such as arsenic and antimony, present in the feed material. Hydrometallurgical processing routes are generally more energy consuming than smelting.
The three dominant pyrometallurgical routes for high-grade copper sulfide concentrates are smelting to a matte followed by converting to blister copper, direct to blister smelting and roasting. The efficiency of the smelting technology is determined by, amongst other things, the Cu/S ratio and the concentration of slag forming components, especially iron, magnesium and silica. Conventional smelting processes are generally not applicable to lower grade or dirty copper concentrates. Not all of the copper content of the original feed is recovered as blister copper, the remaining copper reporting to the slag and to the smelter dusts or fumes recovered from the smelter off-gases. Impurity elements such as arsenic in the feed concentrate can contaminate the smelted copper and increase costs of refining, and may accumulate in smelter dusts and so present occupational hygiene hazards.
Roasting of copper concentrates requires the conversion of the copper content to a water-soluble or sulfate form, which is recovered from the roaster calcine by leaching, followed by solvent extraction and electrowinning. Roasting is often inefficient because copper-containing insoluble ferrite phases can form during the roasting stage and lock some copper and valuable by-products such as cobalt. Impurity elements such as arsenic in the feed concentrate to roasters can follow the vent gasses, or report to separate dust stream which is costly to treat or dispose.
Many hydrometallurgical processes have been proposed for treating copper-containing concentrates. Few of the proposed processes have attained full-scale commercial development. Most hydrometallurgical processes for the recovery of copper from copper concentrates struggle to compete economically against pyrometallurgical steps such as smelting. There are a number of reasons for this including the cost of power, effective control of impurity elements in treated concentrate, problems of effluent treatment or disposal, and difficulty in precious metal recovery.
The recovery of copper from chalcopyrite-containing copper concentrate that also contains appreciable arsenic, i.e. greater than 0.5%, or other pnictogen impurity content is problematic. High temperatures (and pressures) are required to efficiently solubilise the copper during hydrometallurgical treatment. Whilst most of the arsenic will report to the residue, small quantities will co-report with the copper to the leachate. The recovery of the soluble copper from the leachate requires a solvent extraction circuit, and an electrowinning step, that add to the capital and operating costs.
The dirty copper concentrate can be treated by known hydrometallurgical technologies. The descriptions of processes which remove arsenic and other impurity metals from dirty concentrates, and so produce relatively clean concentrates, are referred to in U.S. Pat. No. 3,709,680 Holmes and Coltrinari, and U.S. Pat. No. 3,911,073 Nadkarni, Kusin and Heissner, and Australian Patent No AU 2011318324 Nakon and Way.
The descriptions of processes which involve alkaline leaching, particularly for removal of arsenic or recovery of antimony, are widely published. Recent literature describes various processes e.g. C. Anderson, L. Twidwell, 2008. The Alkaline Sulfide Hydrometallurgical Separation, Recovery And Fixation Of Tin, Arsenic, Antimony, Mercury And Gold, The Southern African Institute of Mining and Metallurgy, Conf, Lead and Zinc 2008; A Shibayama, etal, 2010. Removal Of Arsenic In Enargite From Copper Ores By Flotation And Leaching In NaHS Media, XXV International Mineral Processing Congress Proceedings, Brisbane. G Long, Y Peng, D Bradshaw. 2012. A review of copper-arsenic mineral removal from copper concentrates, Minerals Engineering 36-38 (2012) 179-186.
The flow-sheets disclosed in these patent specifications and process descriptions contain several deficiencies or inefficiencies, such as:                a) additional dosing of costly sodium or sodium-based reagents; sodium sulphide (NaS), or sodium hydro-sulphide (NaHS) and hence recovering, recycling, controlling or discarding expensive reagents;        b) completely oxidised arsenic in the form of arsenate which tends to carry sodium, and so results in a loss of expensive reagent;        c) incomplete extraction of the arsenic and antimony from the copper concentrate and so the concentrate attracts penalties from purchasers;        d) potential loss of precious metals from the concentrate following their dissolution in the strong caustic sulphide leach liquors; and,        e) the pnictogenic elements such as arsenic and antimony may not be disposed into environmentally acceptable stream or condition, and so the final destination or treatment route of residues and effluents may be problematic.        
The present invention was developed with a view to providing a hydrometallurgical process for the removal of impurity elements including arsenic and antimony from a “dirty” copper concentrate that is less susceptible to the above deficiencies which otherwise limit or penalise the processing of the concentrate in a smelter. The process substantially relieves the inefficiencies by advantageously regenerating the leach liquors, thus economising sodium-based reagent inputs. Advantageously the process also precipitates arsenic and antimony into a separate disposable stream.
References to prior art in this specification are provided for illustrative purposes only and are not to be taken as an admission that such prior art is part of the common general knowledge in Australia or elsewhere.